Inorganic perovskite-based active multifunctional integrated photonic devices

The development of highly efficient active integrated photonic circuits is crucial for advancing information and computing science. Lead halide perovskite semiconductors, with their exceptional optoelectronic properties, offer a promising platform for such devices. In this study, active micro multifunctional photonic devices were fabricated on monocrystalline CsPbBr3 perovskite thin films using a top-down etching technique with focused ion beams. The etched microwire exhibited a high-quality micro laser that could serve as a light source for integrated devices, facilitating angle-dependent effective propagation between coupled perovskite-microwire waveguides. Employing this strategy, multiple perovskite-based active integrated photonic devices were realized for the first time. These devices included a micro beam splitter that coherently separated lasing signals, an X-coupler performing transfer matrix functions with two distinguishable light sources, and a Mach-Zehnder interferometer manipulating the splitting and coalescence of coherent light beams. These results provide a proof-of-concept for active integrated functionalized photonic devices based on perovskite semiconductors, representing a promising avenue for practical applications in integrated optical chips.


Part 1
Supplementary Fig. S1 | (a-d In order to assess the extent of the damage caused by focused ion beam (FIB) etching, we characterized the photoluminescence (PL) emission and time-resolved PL (TRPL) delay dynamics of the monocrystalline CsPbBr3 thin film and microstructure (after FIB treatment), respectively, as shown in Fig. S1.The nearly consistent shape and strength of the PL emission before and after FIB treatment demonstrate the feasibility of fabricating photonic devices directly (Fig. S1a     and c).As for the TRPL lifetime, one can observe the two shorter different time scales which are attributed to the radiative recombination of intrinsic excitons (slow) and the bimolecular recombination process of excitons (fast) after FIB treatment, indicating more carrier trap defects are formed under higher ion-dose irradiation (Fig. S1b and d) 1- 3 .It should be noted that our active integrated photonic devices operate in the lasing region (coherent emission), and then utilize such generated microlaser to realize the manipulation of waveguide coupling and propagation.Therefore, such a small number of carrier trap defects has little impact on the function of the devices and the concept we proposed.Supplementary Fig. S2 |  To further analyze the surface elemental composition and chemical state, we performed X-ray photoelectron spectroscopy (XPS) measurement on the monocrystalline CsPbBr3 thin film.The XPS peaks of single Cs3d, Pb4f, and Br3d are collected as shown in Fig. S3.Two peaks at around 738.2 eV and 724.To investigate the cavity geometry-dependent lasing performance, we have measured the lasing properties of the multiple different length CsPbBr3 microwires, as shown in Fig. S5.
Figure S5a displays the top view SEM images of five etched different-length CsPbBr3 microwires, with the dimensions of 6 μm × 3 μm, 8 μm × 3 μm, 10 μm × 3 μm, 15 μm × 3 μm and 20 μm × 3 μm, respectively.All the microwires exhibit smooth surfaces and sharp edges with an identical thickness of 457 nm (Fig. S5d).Under the excitation by a 400 nm femtosecond pulsed laser above the threshold, the PL microscope images reveal that strong lasing emissions distinctly leak out from the opposite end facets of the microwires, which can be attributable to the FP mode oscillation (Fig. S5b).The normalized lasing emission spectra for the five different-length microwires are shown in Fig. S5c, demonstrating the evolution of the lasing mode number versus the length.
The lasing mode numbers increase from 2 to 6 when the lengths of microwires change from 6 μm to 20 μm (Fig. S5e).Thus, we can precisely control the number of output lasing modes by adjusting the length of the FP microcavity.To compare the change of lasing threshold, we set the threshold for microwire with the dimension of 6 μm × 3 μm as P0, and calculated the threshold ratio of these different-length microwires.One can see that lasing thresholds of perovskite microwires exhibit a decay trend with the length increasing, which could be attributed to the enlarged gain medium region (Fig. S5f).Supplementary Fig. S6 |  To investigate the cavity geometry-dependent lasing performance, we have measured the lasing properties of the multiple different width CsPbBr3 microwires, as shown in Fig. S6.
Figure S6a shows the top view SEM images of five different-width microwires, with the dimensions of 15 μm × 0.5 μm, 15 μm × 1 μm, 15 μm × 2 μm, 15 μm × 3 μm and 15 μm × 4 μm, respectively.All the microwires process smooth surfaces and sharp edges with an identical thickness of 444 nm (Fig. S6d).Excited by a 400 nm femtosecond pulsed laser above the threshold, one can see that such microwires display strong lasing emissions in the same type, which distinctly leak out from the opposite end facets and originate from the FP oscillation modes (Fig. S6b). Figure S6c displays the normalized lasing emission spectra for the five different-width microwires, demonstrating the evolution of the lasing mode number versus the width.Unlike the results of the different length microwires, due to the length limitation of the FP microcavity, the number of lasing modes is stable around 5 with the change of width (Fig. S6e).As for the variation trend of the lasing threshold, similarly, we set the threshold for microwire with the dimension of 15 μm × 0.5 μm as P1, and calculated the threshold ratio of these different width microwires.The results also indicate that the thresholds of the perovskite microwires exhibit a decay trend with the width increasing, attributed to the enlarged gain medium region (Fig. S6f).Supplementary Fig. S7 | (a An etched CsPbBr3 microdisk with whispering gallery mode (WGM) for lasing has been still investigated to compare the effect of the cavity geometry on lasing oscillation modes, as shown in Fig. S7.
Figure S7a shows the top view SEM image of the obtained CsPbBr3 microdisk after FIB treatment, where the disk has a smooth surface with a diameter of 8 μm.Also, the smooth surface and sharp edges of the microdisk can be verified from the magnified SEM image, and the thickness is extracted as 466 nm (Fig. S7b).At room temperature, under low-power excitation by a 400 nm femtosecond pulsed laser, the whole disk presents a near-uniform PL emission (Fig. S7c).Under high pump fluence and above the threshold, strong PL emission appears around the disk, which is visibly distinguished from emission in the in-plane region and indicates the WGM mode laser arises (Fig. S7d).
Figure S7e displays the PL emission evolution with the pump fluence of the microdisk.
One can see that with the pump fluence increasing from 51 μJ cm -2 to 66 μJ cm -2 , several sharp peaks of lasing emission emerge at the low-energy side of spontaneous emission, and become dominant in the PL spectra with the intensity rapidly rise.A nonlinear process of the lasing emission in the microdisk is revealed by the evolution of the integrated PL intensity and linewidth as functions of pump fluence (Fig. S7f).The dramatical decrease of the linewidth and the typical S-shaped growth curve of the PL intensity unambiguously indicate the arising of lasing behavior with the pump fluence increasing.Here, the critical threshold of the microdisk is extracted as 53.8 μJ cm -2 .The optical stability of microwire lasers is crucial for the efficient operation of integrated photonic devices.We measured the lasing properties of five CsPbBr3 microwires of the same size to investigate the stability and uniformity of the designed laser devices, as shown in Fig. S8.
As shown in Fig. S8a and b, a typical etched CsPbBr3 microwire exhibits a smooth surface and sharp edges with a dimension of 10 μm × 2 μm × 0.444 μm.Under lowpower excitation by a 400 nm femtosecond pulsed laser, the PL microscope image of the microwire reveals a uniform green-color emission (Fig. S8c).When the pump fluence increases above the threshold, strong lasing emission is observed to distinctly leak out from the opposite end facets of the microwire, owing to the FP mode oscillation (Fig. S8d).The normalized lasing emission spectra for the five microwires of identical dimensions are shown in Fig. S8e, demonstrating the near-unanimous peak shape and number of lasing modes.One can observe that under the same measurement configuration, the thresholds of these microwire lasers exhibit small fluctuation, which also indicates the uniformity of the designed laser devices (Fig. S8f).
Moreover, we performed measurements for the stability and robustness of microwire laser.The emission intensity as a function of pump fluence is measured a few days after the first measurement.One can observe that the emission intensity and threshold of lasing have hardly changed much, as shown in Fig. S8g.Furthermore, we measured the power-dependent emission intensity by repeatedly increasing and decreasing pumping power, and we still observed that the lasing did not degenerate, as shown in Fig. S8h.Thus, we believe the etched perovskite microwire laser is stable and robust under high optical excitation.
(a) Atomic force microscopy image of a monocrystalline CsPbBr 3 thin film, showing a typical thickness of 410 nm.Scale bar: 1 μm.(b) High-resolution transmission electron microscopy (TEM) image of the monocrystalline CsPbBr 3 thin film, demonstrating the lattice spacing 4,5 of 0.29 nm.Scale bar: 5 nm.(c-f) Cross-sectional TEM image and energydispersive X-ray spectrometry elemental mappings of the monocrystalline CsPbBr 3 thin film, revealing a uniform spatial distribution of Cs, Pb, and Br elements.Scale bar: 50 nm.(g) Microregion (a range of 200 micrometers) XRD of a monocrystalline CsPbBr 3 thin film, showing the orthorhombic phase structure 4,6 and good monocrystalline property.The XRD peak originating from the pure mica substrate is marked by *.The inset shows the magnified tiny splitting XRD peaks of the sample at ~ 30.7°.Supplementary Fig. S3 | (a-c) XPS analysis of the monocrystalline CsPbBr 3 thin film for Cs 3d (a), Pb 4f (b), and Br 3d (c), respectively.The presence of Cs, Pb and Br elements is consistent with the material composition of CsPbBr 3 .
3 eV can be assigned to Cs 3d3/2 and Cs 3d5/2, while the strong peaks located at 143.0 eV and 138.1 eV are attributed to Pb 4f5/2 and Pb 4f7/2, respectively.The prominent peaks of Br 3d3/2 and Br 3d5/2 of Br3d are observed at around 69.1 eV and 68.0 eV.Meanwhile, analysis of the presence of Cs, Pb, and Br elements is nearly consistent with the material composition of CsPbBr3, demonstrating the high chemical purity of the CsPbBr3 thin film on mica through direct CVD synthesis.Supplementary Fig. S4 | Scanning electron microscopy (SEM) images of the CsPbBr 3 microwire after FIB treatment, showing the smooth surface and sharp edges to form a transverse Fabry-Pérot (FP) microcavity 7-9 and a height of 525 nm.(a) Side facet.(b) End facet.Scale bar: 500 nm.Tilted by 50° with respect to the horizontal position for (a-b).Supplementary Fig. S5 | (a) SEM images of CsPbBr 3 microwires with identical widths of 3 μm and different lengths from 6 μm to 20 μm.Scale bar: 4 μm.(b) Corresponding PL microscope images of the different-length microwires above the threshold.Scale bar: 4 μm.(c) The normalized lasing emission spectra of the different-length microwires above the threshold.(d) SEM image of the side facet for one microwire (tilted by 50° with respect to the horizontal position), indicating a height of 457 nm.Scale bar: 300 nm.Such microwires are of identical thickness.(e) Evolution of the lasing mode number as a function of the length of microwire.(f) Evolution of the lasing threshold as a function of the length of microwire, setting the threshold of microwire with the dimension of 6 μm × 3 μm as P 0 .
(a) SEM images of CsPbBr 3 microwires with identical lengths of 15 μm and different widths from 0.5 μm to 4 μm.Scale bar: 4 μm.(b) Corresponding PL microscope images of the different-width microwires above the threshold.Scale bar: 4 μm.(c) The normalized lasing emission spectra of the different-width microwires above the threshold.(d) SEM image of the side facet for one microwire (tilted by 50° with respect to the horizontal position), indicating a height of 444 nm.Scale bar: 300 nm.Such microwires are of identical thickness.(e) Evolution of the lasing mode number as a function of the width of microwire.(f) Evolution of the lasing threshold as a function of the width of microwire setting the threshold of microwire with the dimension of 15 μm × 0.5 μm as P 1 .

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SEM image of a CsPbBr 3 microdisk with a diameter of 8 μm after FIB treatment.Scale bar: 4 μm.(b) SEM image of the side facet for the microdisk (tilted by 50° with respect to the horizontal position), indicating a height of 466 nm.Scale bar: 400 nm.(c-d) Corresponding real-space PL images of the microdisk below (c) and above (d) the threshold, respectively.Scale bar: 4 μm.(e) PL spectra emitted from the microdisk with the pump fluence increasing from 51 μJ cm -2 to 66 μJ cm -2 .(f) Evolution of the integrated PL emission intensity (red curve) and linewidth (blue curve) as functions of pump fluence of the microdisk, showing the threshold of 53.8 μJ cm -2 .(g) One magnified lasing oscillation mode with a Lorentz-fitted linewidth of 0.198 nm and a Q-factor of 2718.

Figure
FigureS7gillustrates the Lorentz fitting of one magnified lasing oscillation mode with a linewidth of 0.198 nm and a Q-factor of 2718 at 1.12 Pth, indicating the high lasing performance of the etched perovskite microdisk.